Parkinson’s disease (PD) is a progressive disease of the central nervous system that involves the degeneration of neurons that release the neurotransmitter dopamine. These neurons  project into the striatum from a specialized region of the mid-brain called the substantia nigra, (black substance, due to its colour). Dopamine acts on neurons in the basal ganglia (putamen and nucleus caudatus) where, interacting with other neurotransmitters such as acetylcholine, GABA, and glutamate assures smooth initiation and execution of movements. The shortage of dopamine results in a number of symptoms, including resting tremors, generalised slowness, stiffness of the limbs and gait or balance problems and more in general changes in the ability to produce smooth, consistent, controlled muscular activity.

The disease is progressive, often beginning with just a hand tremor, lessened facial expression, mild fatigue or stiff arms or legs, but becoming increasingly debilitating. Typically only one side of the body is affected which spreads to the other side as the disease progresses. Rigidity and slow movements of all muscles affect mobility, coordination, balance and posture. It is unclear how or why the dopamine neurons selectively die or degenerate in PD. Probably free radicals, toxins and genetic factors are all involved to some extent.

Cognitive impairment is also a characteristic of the disease, which occurs even in non-demented and early-stage PD patients. It has been clearly recognised that in PD there are deficits related to attention, alertness, perception, motivation, intelligence and finally cognition and memory. These deficits in a large percentage of patients, in particular in early PD patients, are not extensive and are not severe enough to be classified as dementia. Moreover in a high percentage of these patients the deficits do not progress to dementia. In some individuals cognitive decline can develop in the presence of mild Parkinson disease-related cortical pathology and, conversely, widespread cortical lesions do not necessarily lead to cognitive decline.

There is no known cure for Parkinson’s disease. The treatments available are aimed at alleviating symptoms such as dopamine agonists or dopamine precursors. By replenishing dopamine levels in the brain or reinforcing dopamine tone in the needed areas, motor symptoms improve. Other types of treatment for Parkinson’s disease are being developed: these include stimulation of deep brain structures, which is becoming widely accepted to treat severe complications late in the disease, attempt to replace lost cells with implant of cells types known to produce dopamine. With advancing disease in most cases treatment becomes more difficult with patients ending up taking several different drugs.

Many people do not recognize the early symptoms of Parkinson’s disease, as they simply attribute them to aging, and for this reason there are probably a significant number of people with undiagnosed Parkinson’s disease. The proportion of people older than 60 years with the disease is approximately 1% (Lancet, 2004) however, as people continue to live longer, a larger number of people are likely to reach this age, resulting in more people suffering from this and other diseases that affect the elderly.